1. Field of the Invention
This invention relates to liquid pressure measurements and more particularly, to related density measurements by measuring the difference in pressure in a quantity of liquid between a first and second vertical location.
2. Description of the Prior Art
Huge fluid systems, such as exemplified by mud systems of an oil well drilling operation, often need to be closely and continuously monitored for variation in conditions. By monitoring such parameters as the density or change of density over a period of time of such a system, it is possible to deduce what is occurring with the environment or the procedure supported by the liquid system. For example, the infusion of gas or salt water from the formation will change the density of the liquid in the system. Likewise, the settling, addition or extraction of suspended particulates will also cause a resulting change in the fluid density of the system.
A popular procedure for measuring density of liquids uses a sampling densitometer. Although accurate and convenient in some contexts, it necessarily only provides sampling of a limited quantity of the liquid, which may not be homogeneous throughout the larger quantity from which the sample is drawn. Further, such a measurement is a measurement of intermittent conditions and does not provide a continuous readout.
A more suitable procedure for measuring density or changes in density of a large liquid system is provided by the employment of a pressure differential gauge, the pressure sampling being taken at two different vertical locations within the liquid quantity. One of the best and most reliable of such devices is disclosed in patent application Ser. No. 06/371.789, "Method and Apparatus for Gauging Liquid Filled Tanks", filed Apr. 26, 1981 by the same inventor, now U.S. Pat. No. 4,446,730 which is incorporated herein by reference for all purposes.
It has heretofore been believed that the pressure-sensitive element or elements, usually in the form of a diaphragm or diaphragms employed in a pressure sampling device, were necessarily preferably oriented to be in horizontal planes. This is because the pressure at a given vertical location within a quantity of liquid is at the same pressure level. Therefore, if the sampling diaphragm were oriented horizontally, it would effectively be measuring the pressure in that horizontal plane. On the otherhand, a vertically oriented diaphragm would cause sampling to occur at some inexact pressure location between the top and bottom of the diaphragm. That is, the top of the diaphragm would be at one pressure and the bottom of the diaphragm would be at a different pressure. This is because the pressure varies with depth of the liquid. Due to the flexing characteristics of the diaphragm, the actual pressure level would not reliably be in a centered position between top and bottom, but at a location that even varies with the amount of pressure in contact therewith.
However, it may be recognized that liquid systems, such as a mud system, that are best monitored by continuously measuring and indicating devices, are by definition dynamic, ever-changing systems, as opposed to static or calm systems. Such systems are often turbulent. When confined, the swirling turbulence in the vertical direction is much greater than the wave action from side to side. Hence, a horizontally-oriented diaphragm is subject to such predominant turbulence, causing fluctuating and even false readings to result.
Although it is possible to place a barrier in front of a horizontal diaphragm to eliminate some of the turbulent action from affecting the pressure sensing, such a barrier is unsatisfactory in the presence of sediment or solid particles. This is because such sediment will build up on the barrier and, in time, if sufficiently close to the diaphragm to be an effective shield against turbulence, will even accumulate to the extent that it will prevent free movement of the diaphragm. This will cause false and unacceptable readings to result.
Therefore, it is a feature of the present invention to provide an improved device for measuring pressure in a quantity of liquid wherein one or more vertically oriented membranes are used, but in such a manner that the pressure is measured at precise vertical location(s).
It is another feature of the present invention to provide an improved device for measuring the difference in pressure in a quantity of liquid between a first and a second vertical location wherein vertically oriented membranes are used, but in such a manner that the pressure differential is precise with respect to such locations.
It is yet another feature of the present invention to provide an improved device for pressure measurement in a liquid employing vertically oriented membranes that are protectable from turbulence by a vertical barrier which is not susceptible to sediment build-up in the manner of a horizontally oriented barrier.